Some micro-electromechanical systems (“MEMS”) operate by driving a movable member into oscillation. For example, in a MEMS gyroscope, a drive signal is applied to a MEMS structure to force the structure into oscillation, preferably at its resonant frequency. The MEMS structure imparts a phase shift on the drive signal. The magnitude of the phase shift is a function of the proximity of the oscillating frequency of the structure to its resonant frequency. A phase locked loop (“PLL”) in the drive circuitry processes the phase data to adjust the drive frequency towards the resonant frequency. A PLL in the drive circuitry can, once it achieves phase lock, assist in maintaining the oscillation at the desired frequency.